The present invention is in the field of biological control of insect pests, specifically in the area of use of entomopathogenic fungi for the control of flying insects.
Control of the house fly is of major economic importance throughout the world because of public health concerns. The fly has the potential to mechanically transmit a wide variety of human pathogens, as reviewed by Bida Wid, S. P., J. I. Braim and R. M. Matossian, Ann. Trop. Med. Parasitol. 72(2): 117-121 (1978). The fly can also be annoying to people, livestock and poultry, to the extent that it even decreases time spent by animals in feeding, thereby decreasing feed efficiency.
Because of the economic and public health importance of the house fly, a significant amount of effort has been devoted to develop methods to control it. The biggest effort has been directed towards chemical insecticides, as reviewed by J. G. Scott and D. A. Rutz, J. Econ. Entomol. 81(3): 804-807 (1988). The use of chemical insecticides has a number of serious drawbacks, such as the destruction of non-target biological control agents, development of insecticide resistance, harmful levels of insecticide residue and environmental pollution. Therefore, it is desirable to have less ecologically-disruptive means to control house flies.
New approaches to fly control include the use of parasitoid wasps of various genera, as reported by J.D. Mandeville, et al. Can Ent 120: 153-159 (1988). This method of control reduces the fly population but is not adequate in itself to provide satisfactory fly control.
Insect pathogens are a possible alternative to the common use of highly toxic chemical insecticides for the control of insect pests. Fungi are one of the promising groups of insect pathogens suitable for use as biological agents for the control of insects.
Fungi are found either as single cell organisms or as multicellular colonies. While fungi are eukaryotic and therefore more highly differentiated than bacteria, they are less differentiated than higher plants. Fungi are incapable of utilizing light as an energy source and therefore restricted to a saprophytic or parasitic existence.
The most common mode of growth and reproduction for fungi is vegetative or asexual reproduction which involves sporulation followed by germination of the spores. Asexual spores, or conidia, form at the tips and along the sides of hyphae, the branching filamentous structures of multicellular colonies. In the proper environment, the conidia germinate, become enlarged and produce germ tubes. The germ tubes develop, in time, into hyphae which in turn form colonies.
One would expect that pathogens had been extensively considered as biological control agents, however, a review of the literature reveals the scarcity of pathogens that appear to offer potential to control M. domestica. The bulk of scientific literature on associations of pathogens with house flies refers to isolated reports of diagnosis of dead flies or laboratory studies without practical, short-term applications.
An extensive review of the literature reveals only isolated cases of fungal infection (see, for example, Table 1 in Briggs and Milligan, Bull. World Health Organization 58(Supplement): 245-257 (1980); Briggs and Milligan, Bull. World Health Organization 55(Supplement): 129-131 (1977)). Most reports of fungi associated with flies appear to refer to situations where the fungi did not cause patent infections or major predictable collapses of fly populations. Therefore, it does not appear as though fungi can be practically used for fly control. For example, although the fungi Aspergillus niger, A. flavus, A. ustus and Mucor racemosus from pupae or adults of M. domestica by Zuberi, et al., Pakistan J. Sci. Ind. Res. 12, 77-82 (1969) there was no evidence that these fungi were inflicting serious pathological effect on the fly populations.
It is possible to infect adult house flies with fungi under certain laboratory conditions, leading to death of the infected flies. For example, Aspergillus flavus was pathogenic to M. domestica when the insects were fed high concentrations (up to 1.times.10.sup.9) of fungal spores, presumably due to toxins in the spores. Mortality after seven days of exposure was 57%; mortality was 100% twenty-one days after exposure. One hundred percent mortality occurred in flies seven days after they were anesthetized and placed in contact with fungal spores, as reported by Amonker and Nair, J. Invertebr. Pathol. 7: 513-514 (1965). Dresner, J. N.Y. Entomol. Soc. 58: 269-279 (1950), also reported that an isolate of the fungus Beauveria bassiana infected adult M. domestica when the insects were exposed to a dust of germinating conidia adhered in a nutrient medium. The fungus was also infective to flies when the insects were exposed to a dish of milk containing fungal conidia.
D. C. Rizzo conducted studies, reported in J. Invert. Pathol. 30, 127-130 (1977), on the mortality of flies infected with either Metarhizium anisopliae or Beauveria bassiana and determined that the time to death after infection was independent of age. Flies were infected by rolling them for ten minutes in four-week-old fungal culture slants until they were completely exposed to the spores, then maintaining them in humidity chambers. As noted by the author, in reference to the infecting fungi, "these pathogens have never been reported as having caused mycoses in fly populations in nature" at page 127.
In 1990, however, D. C. Steinkraus, et al., reported in J. Med. Entomology 27(3), 309-312, that Musca domestica L., infected with Beauveria bassiana had been found on dairy farms in New York, although at a prevalence of less than 1% (28 out of 31,165). Isolates of the fungi were infective for laboratory raised flies, but the low naturally occurring incidence led to the conclusion by the authors that "it seems unlikely that these infections represent naturally occurring epizootics within house fly populations" at page 310.
These studies have led to the recognition that there is a potential for fungal control of insects. However, no one has yet developed a consistent and commercially viable way of infecting insects and assuring that the fungi are dispersed throughout the breeding populations. For example, with reference to house flies, it is clearly impractical, and will make the registration of any product with the Environmental Protection Agency in the United States very difficult, to disperse conidia on surfaces or dishes of nutrient media whenever there is a need to control the fly population.
As of this time, there has been no successful demonstration by others of the practical, reliable and economical employment of an entomopathogenic fungus for the management and biological control of flying insects such as the common housefly.
It is therefore an object of the present invention to biologically control flying insects, especially the housefly, using entomopathogenic fungi.
It is a further object of the present invention to provide a device for the convenient, reliable and economically feasible application of fungi in the biological control of flying insects.